P394: INSIGHTS INTO PATIENT-DERIVED XENOGRAFT MODELS FOR DEK-NUP214 LEUKEMIA
Authors: F. Charles Cano, A. Kloos, T. Fangmann, N. Kattre, R. Schottmann, K. Döhner, A. Ganser, M. Heuser
Journal: HemaSphere (2022)

Background: Acute myeloid leukaemia (AML) with the translocation DEK-NUP214 (t(6;9)(p23;q34)) is a rare subtype present in 1% of adult and 2% of paediatric patients and is recognized by the world health organization (WHO) as a unique subgroup of AML. These patients, typically, are diagnosed with de novo AML and have poor clinical outcome and resistance to chemotherapy. DEK-NUP214 is the sole cytogenetic abnormality in the majority of these patients at the time of diagnosis, suggesting its central role in disease development. This subgroup of leukaemia remains poorly characterized. There is only one cell line (FKH-1) and only very few reported DEK-NUP214 patient derived xenograft (PDX) models. The major limitation is the lack of serially transplantable PDX models, which are required for pharmacologic studies. The development of DEK-NUP214 PDX models will aid in the understanding of the molecular pathogenesis of this disease. Aims: To establish patient-derived xenograft models that recapitulate DEK-NUP214 leukaemia. Methods: Five patient samples were selected based on their cytogenetic profile and 1x106 cells were injected intravenously into irradiated NSG-SGM3 (NSGS) mice (n=3) per sample. Engraftment of human cells in peripheral blood by flow cytometry and blood counts was monitored monthly. Engrafted cells were used for serial transplantations. Cytospin preparations of peripheral blood, spleen and bone marrow of the PDX samples as well as the patient samples were stained with Wright-Giemsa stain. The DEK-NUP214 fusion transcript was confirmed by Sanger sequencing. Mutational analysis was performed with a custom myeloid sequencing panel. Results: Three patient samples showed a mean of 12.5±6.0 (PDX1), 0.68±0.23 (PDX2) and 4.9±2.5% (PDX3) engraftment of human CD45+CD33+ cells at 20-24 weeks in peripheral blood and were transplanted into secondary mice. The characteristics of the patients at diagnosis, whose samples engrafted, were 19, 53 and 51 years old, respectively, with a median of 52.8 x109/L (range 34.1-116 x109/L) white blood cells (WBC), 7.4 g/dl (range 6-9.4 g/dl) of haemoglobin (Hb), and 38 x109/L (range 26-61 x109/L) platelets (Plt). The average circulating blasts were 56.7±18% in peripheral blood and blasts in bone marrow were 84.7±4.7%. PDX models at the 1st transplantation (Tx) had an increased WBC and decreased Hb at the time of sacrifice. Average spleen weights were 196±24.1, 59.7±3.18, and 103±35.4 g, respectively. The morphological analysis revealed large blasts with partially granulated cytoplasm and few vacuoles similar to the patients’ cells. The engrafted cells showed a myeloid phenotype with expression of CD38, CD33 and CD14, with higher engraftment in bone marrow than spleen. Secondary transplants from PDX1 showed 12.5% of hCD45+ cells at 16 weeks in peripheral blood, with average spleen weight of 168 g, with a similar immunephenotype as primary mice, and were transplanted into tertiary mice. Mutational analysis showed that the PDX samples retained the same mutations as observed in the patient sample (FLT3-ITD for PDX1 and PDX2, and WT1 for PDX1) and the fusion transcript as well. Summary/Conclusion: We have successfully established AML PDX models for DEK-NUP214 leukaemia that reflect the morphological, immunophenotypic and molecular genetics of this disease subtype. This will enable pharmacologic studies in this rare disease and will allow a better understanding of the involved pathways.